The present invention relates generally to inkjet printing mechanisms, and more particularly to a tapered screw spittoon system for handling waste inkjet ink that has been spit from an inkjet printhead during a nozzle clearing, purging or xe2x80x9cspittingxe2x80x9d routine.
Inkjet printing mechanisms use cartridges, often called xe2x80x9cpens,xe2x80x9d which eject drops of liquid colorant, referred to generally herein as xe2x80x9cink,xe2x80x9d onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, ejecting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).
To clean and protect the printhead, typically a xe2x80x9cservice stationxe2x80x9d mechanism is supported by the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which substantially seals the printhead nozzles from contaminants and drying. Some caps are also designed to facilitate priming, such as by being connected to a pumping unit that draws a vacuum on the printhead. During operation, clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a process known as xe2x80x9cspitting,xe2x80x9d with the waste ink being collected in a xe2x80x9cspittoonxe2x80x9d reservoir portion of the service station. After spitting, uncapping, or occasionally during printing, most service stations have an elastomeric wiper that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead. The wiping action is usually achieved through relative motion of the printhead and wiper, for instance by moving the printhead across the wiper, by moving the wiper across the printhead, or by moving both the printhead and the wiper.
As the inkjet industry investigates new printhead designs, one trend is toward using a xe2x80x9csnapperxe2x80x9d reservoir system where permanent or semi-permanent printheads are used and a reservoir carrying a fresh ink supply is snapped into place on the printhead. Another new design uses permanent or semi-permanent printheads in what is known in the industry as an xe2x80x9coff-axisxe2x80x9d printer. In an off-axis system, the printheads carry only a small ink supply across the printzone, with this supply being replenished through tubing that delivers ink from an xe2x80x9coff-axisxe2x80x9d stationary reservoir placed at a remote stationary location within the printer. Narrower printheads may lead to a narrower printing mechanism, which has a smaller xe2x80x9cfootprint,xe2x80x9d so less desktop space is needed to house the printing mechanism during use. Narrower printheads are usually smaller and lighter, so smaller carriages, bearings, and drive motors may be used, leading to a more economical printing unit for consumers.
These snapper and off-axis inkjet systems are described in contrast with what is known as a xe2x80x9creplaceable cartridgexe2x80x9d system, which supply a disposable printhead with the ink supply in an inkjet cartridge, so when the reservoir is emptied, the entire cartridge including the printhead is replaced. A replaceable cartridge system assures the customer has a fresh, new printhead each time the ink supply is replaced. Some replaceable cartridges are monochrome (single color), for instance, carrying only black ink, while other cartridges are multi-color, typically carrying cyan, magenta and yellow inks. Some printing mechanisms use four monochrome cartridges, while others use a black monochrome cartridge in combination with a tri-color cartridge.
To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide quicker, more waterfast printing with darker blacks and more vivid colors, pigment-based inks have been developed. These pigment-based inks have a higher solid content than the earlier dye-based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to form high quality images on readily available and economical plain paper, as well as on recently developed specialty coated papers, transparencies, fabric and other media. However, the combination of small nozzles and quick-drying ink leaves the printheads susceptible to clogging, not only from dried ink or minute dust particles, such as paper fibers, but also from the solids within the new inks themselves.
When spitting these new pigment-based inks onto the flat bottom of a conventional spittoon, over a period of time the rapidly solidifying waste ink grew into a stalagmite of ink residue. Eventually, in prototype units, the ink residue stalagmite grew to contact the printhead, which then either could interfere with printhead movement, print quality, or contribute to clogging the nozzles. Indeed, these stalagmites even formed ink deposits along the sides of the entranceway of prototype narrow spittoons, and eventually grew to meet one another and totally clog the entrance to the spittoon. To avoid this phenomenon, conventional spittoons had to be wide enough to handle these high solid content inks. This extra width increased the overall printer width, which then defeated the narrowing advantages realized by using an off-axis printhead system.
A ferris wheel spittoon system was disclosed in U.S. Pat. No. 5,617,124, currently assigned to the present assignee, the Hewlett-Packard Company. This system proposed an elastomeric ferris wheel as a spit surface. Ink residue was removed from the wheel with a rigid plastic scraper that was oriented along a radial of the wheel so the scraper edge approached the spitting surface at a substantially perpendicular angle. The scraper was located a short distance from the surface of the wheel, so it unfortunately could not completely clean the spitting surface. Furthermore, by locating the scraper a distance from the spit surface, the scraper was ineffective in removing any liquid ink residue from the wheel. This earlier ferris wheel spittoon system failed to provide for adequate storage of the ink residue after removal from the ferris wheel during the desired lifespan of a printer. One adaptation of the ferris wheel spittoon used a plastic scraper to remove the ink residue from the wheel in a spaghetti-like string that was packed in a storage bucket. Unfortunately, this wheel spittoon, scraper and bucket system does not lend itself well to height reduction. Thus, it would be desirable to have a spittoon system which defeats ink residue stalagmite build-up, and provides a low-profile ink residue storage system for the lifespan of the inkjet printing unit.
According to one aspect of the present invention, a spittoon system is provided for handling ink residue spit from an inkjet printhead in an inkjet printing mechanism. The spittoon system includes a reservoir having a first end and an opposing second end. The reservoir defines an entranceway opening adjacent to the first end for receiving ink residue spit from the inkjet printhead. The reservoir also defines an ink exit opening that is located remote from the first end. A tapered screw member is rotatably mounted inside the cylindrical reservoir. The tapered screw member has a tapered shaft which increases in diameter along the length of the screw member from the first end of the reservoir toward the second end of the reservoir. The spittoon system also has a rotating device that selectively rotates the tapered screw member to transport ink residue received through the entranceway opening, and that squeezes the ink residue out of the reservoir through the ink exit opening.
According to another aspect of the present invention, a spittoon system is provided for handling ink residue spit from an inkjet printhead in an inkjet printing mechanism. The spittoon system has a reservoir with a wall having an interior surface that defines a collection chamber. The collection chamber has a first end and an opposing second end. The reservoir defines an entranceway opening adjacent to the first end for receiving ink residue spit from the inkjet printhead, and the reservoir also defines an ink exit opening remote from the first end. An active member is moveably mounted inside the cylindrical reservoir to define a void between the active member and the interior surface of the reservoir wall. This void decreases in cross sectional volume from the first end of the reservoir toward the second end of the reservoir. The spittoon system also has an activator device that selectively moves the active member to transport ink residue received through the entranceway opening through the void to the ink exit opening. The ink residue is compacted during transport through the decreasing in cross sectional volume of the void and squeezed out of the reservoir through the ink exit opening.
According to a further aspect of the present invention, a method of purging ink residue from an inkjet printhead in an inkjet printing mechanism is provided. This method includes the steps of spitting ink residue from the printhead onto a spit region of a compaction member and transporting the ink residue from the spit region to a second location. During the transporting step, in a compacting step the ink residue is compacted with the compaction member. The method also includes the step of expelling the compacted ink residue into a storage container at the second location.
According to a still another aspect of the present invention, method is provided of purging ink residue from an inkjet printhead in an inkjet printing mechanism. This method includes the step of spitting ink residue from the printhead onto a spit region of a spiral member rotationally mounted within a reservoir. In a transporting step, the spit ink residue from the spit region is transported to a second location along a spiral path within the reservoir. The method also includes the step of expelling the ink residue into a storage container at the second location.
According to a further aspect of the present invention, an inkjet printing mechanism may be provided with a spittoon system for handling waste inkjet ink as described above.
An overall goal of the present invention is to provide an inkjet printing mechanism which prints sharp vivid images over the life of the printhead and the printing mechanism.
Still another goal of the present invention is to provide a spittoon system that efficiently removes the waste ink residue from a spitting region and then stores this residue over the expected lifespan of an inkjet printing mechanism.
Another goal of the present invention is to provide a long-life spittoon system for receiving ink spit from printheads in an inkjet printing mechanism to provide consumers with a reliable, robust inkjet printing unit.